... and the desktop zooms out so the entire desktop fits within the overlay. When you select something from the activities menu, or press it again, the overlay closes and the desktop zooms back out to full screen.

This doesn't really come across well in either the screenshot or the text.

Personally I think it is a neat way of exploiting the new graphic capabilities to do something useful.

Since this is a prototype, however, it is very unlikely to look exactly like the screenshot when finished.